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Re: RDDL->RDF (was Re: Draft agenda of 22 February 2005 TAG

From: Stuart Williams <skw@hp.com>
Date: Wed, 23 Feb 2005 16:17:53 +0000
Message-ID: <421CACB1.6070805@hp.com>
To: Dan Connolly <connolly@w3.org>
Cc: "Henry S. Thompson" <ht@inf.ed.ac.uk>, www-tag@w3.org

Dan, Henry,

There is considerable archived discussion of  RDDL and RDF early in the 
life, both in the context of embedding RDF directly in HTML [1] and more 
recently using some from of transformation process (like the XSLT that 
Jonathan provides) to extract RDF [2].

Somewhere in-between there was some discussion at our F2F in Boston Nov 
2002... where Dan did some whiteboard doodles (that are captured in the 
meeting record) about how to model RDDL information content in RDF.

IIRC there is little common agreement about how RDDL information should 
be represented in RDF.

In Jonathan's mapping RDDL natures (which IIRC is derived from Ron 
Daniels work on mappping/extracting RDF from Xlinks) become the object 
values of rdf:type properties associated with an RDF node that 
represents a RDDL directory entry. RDDL purposes are modelled as RDF 
properties whose subject is also the directory entry and whose object is 
the/a related resource with the purpose associated with the 
property/predicate between. The namespace, which is in a sense the 
subject of the entire directory is not explicit in the resulting RDF - 
see the example RDF below. For some that was perfectly fine because 
surely that was self evident from that being the URI used to obtain the 
RDDL in the first place - for others (Dan?) that was not fine, because 
there is nothing in the resulting RDF that associates the collection of 
directory entries [ :DTD,  :xmlshema and :xmlschema1 below] back to the 
namespace that they are directory entries for.

Other suggested approaches have had rddl:purpose and rddl:nature RDF 
properties whose object values have then been purposes and natures.

Various approaches to presenting RDDL information as RDF have been 
discussed through the lifetime of this issue - none seem of have found 
universal enthusiasm (nor necessarily has the notion of having an RDF 
based RDDL syntax ;-) ).

Interestingly, passing the RDF generated by Jonathan transform through 
the W3C RDF validator generates 'interesting' URI's for subjects and 
object that have relative URI references in the generated RDF. 
Particularly, the base URI associated with XMLScheme.dtd and 
XMLSchema.xsd (ie. the namespace name - I think) gets lost and replaced 
with something else :-(

I hope this helps bootstrapping some of the context associated with is 
topic.

Best regards

Stuart
--
[1] http://lists.w3.org/Archives/Public/www-tag/2002Apr/thread.html#69
[2] http://lists.w3.org/Archives/Public/www-tag/2004Jan/thread.html#26
[3] http://www.w3.org/2002/11/18-tag-summary#RDDL

Dan Connolly wrote:

>On Wed, 2005-02-23 at 08:55 +0000, Henry S. Thompson wrote:
>[...]
>  
>
>>  For example,
>>
>>  http://www.w3.org/2001/XMLSchema.html.
>>    
>>
>
>Hmm... OK... I get the following statements
>(converted to turtle syntax
>http://www.ilrt.bris.ac.uk/discovery/2004/01/turtle/
>for clarity)
>
>
>     @prefix : <#> .
>     @prefix ns1: <http://www.rddl.org/purposes#> .
>
>    :DTD     a
><http://www.isi.edu/in-notes/iana/assignments/media-types/application/xml-dtd>;
>         ns1:validation <XMLSchema.dtd> .
>
>    :xmlschema     a <http://www.w3.org/2001/XMLSchema>;
>         ns1:schema-validation <XMLSchema.xsd> .
>
>    :xmlschemap1     a <http://www.w3.org/TR/html4>;
>         ns1:normative-reference
><http://www.w3.org/TR/2004/PER-xmlschema-1-20040318/> .
>
>
>
>(a) why are the subjects of these statements different?
>They should have a common subject, right?
>Does XLink say what URI is the other end of the link
>in these cases? the XLink terminology seems to
>be 'starting resource'...
>
>Hmm...
> [Definition: A local resource is an XML element that participates in a
>link by virtue of having as its parent, or being itself, a linking
>element].
>
>that makes it sound like link resources are syntactic
>elements. I would have thought that the subject
>(aka starting resource?) in this case is the XML Schema
>namespace. The RDDL spec talks about "related resource"s.
>Related _to what_?
>
>
>(b) using an IANA media-types registry entry as an RDF Class...
>hmm... I wonder if IANA means it to be a class. Perhaps
>better to use rddl:nature as the predicate there rather
>than rdf:type.
>
>
>Trying it on http://www.rddl.org/ itself, I see those
>issues plus a syntax error...
>
>  <rdf:Description rdf:about="http://www.rddl.org/#related.resources">
>
>    <rdf:type rdf:resource="http://www.w3.org/1999/XSL/Transform" />
>    <rdf:resource rdf:resource="rddl2rdf.xsl" />
>  </rdf:Description>
>
>
>Using rdf:resource as a property element isn't allowed.
>http://www.w3.org/TR/rdf-syntax-grammar/#propertyElementURIs
>
>I haven't figured out whether that problem comes from
>the input or the transformation.
>
>There also seem to be some (documented) limitations in handling
>of URI references...
>
><!-- 
>	note: assume xlink:arcrole := absoluteURI  '#' fragment-id
>-->
>
>
>p.s.
>
>  
>
>>Dan Connolly <connolly@w3.org> writes:
>>
>>    
>>
>>>On Tue, 2005-02-22 at 17:17 +0000, Henry S. Thompson wrote:
>>>      
>>>
>>>>Further to Item 1.1.3: Review action items 7 Feb [1]:
>>>>
>>>>  ACTION: Henry to produce a RDDL1 to RDF Style sheet or explain why not
>>>>
>>>>I find that Jonathan Borden produced such a stylesheet over four years
>>>>ago [2].  I tried it, it seems to work.
>>>>        
>>>>
>>>I'm curious... tried it with what? I forget which input syntax it
>>>expects. I'll try to get swapped back in, but any help you can provide
>>>is welcome.
>>>      
>>>
>>Any RDDL document.
>>    
>>
>
>Ummm... the TAG has looked at a number of RDDL designs.
>The "current" one, by some measure of current, is
>  http://www.tbray.org/tag/rddl4.html
>and given that document as input, [2] doesn't work; it gives...
>
><?xml version="1.0"?>
><!--RDF generated from RDDL document (http://www.rddl.org/-->
><rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
>xmlns:rddl="http://www.rddl.org/"
>xmlns:xlink="http://www.w3.org/1999/xlink"/>
>
>So please disambiguate the term 'RDDL' more clearly, at
>least for a little while.
>
>  
>
Received on Wednesday, 23 February 2005 16:21:51 GMT

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